206 Brush and Dana — Mineral Locality at Branchville. 



as it has been investigated ; the optic axes lie in basal section 

 and the acute bisectrix (positive) is normal to the brachy- 

 pinacoid. The characteristic basal cleavage is always a promi- 

 nent character, but the bra chy diagonal cleavage 010 is less 

 distinct than is shown by lithiophilite, and the prismatic cleav- 

 age (110) is interrupted; the measured angle was 50°; these 

 cleavages are seen more clearly in thin sections. The fracture 

 is conchoidal, more perfectly so than with lithiophilite. The 

 color is a rather deep wine-yellow, much like that of the Bra- 

 zilian topaz. The luster, is brilliant resinous to nearly adaman- 

 tine ; it was, in fact, the brilliancy of the luster which first 

 attracted our attention, and which is, so far as the eye is con- 

 cerned, its most distinguishing character. The mineral itself 

 is perfectly clear and transparent, but the masses are much 

 fractured and rifted. The surfaces are often covered by a very 

 thin scale of an undetermined mineral, having a fine fibrous, 

 form, a delicate yellowish color and silky luster. This same 

 mineral penetrates the masses wherever there is a fracture 

 surface of cleavage or otherwise. What the exact nature of 

 this mineral is we are unable to say, since the amount is too 

 small to admit of a satisfactory determination — it appears to 

 be a manganesian phosphate. It is evidently an alteration- 

 product and would seem to imply that natrophilite is rather 

 subject to easy chemical change. In any case this silky film is 

 one o£ the characteristic features of the mineral, and directs 

 attention to it at once even over the surface of a hand specimen 

 where it is associated with lithiophilite and perhaps three or 

 four other of these phosphates. 



Before the blowpipe natrophilite fuses very easily and colors 

 the flame intensely yellow, thus being at once distinguished 

 from lithiophilite. It also gives the usual reactions for manga- 

 nese. The following is an analysis of natrophilite made by 

 Wells. The specific gravity on two fragments was found to be 

 3-40 and 342. 



I. 



ii. 



in. 



Mean. 



P 2 6 .. 41-03 







41-03 — 142= -289 = 1 =1 



MnO .. 38-19 

 FeO_„ 3-06 



— 



— 



38-19- 7l=-538 } .ko _ 2 . 01 _ 2 

 306- 72 = -042 \ 580 - 2 01 - 2 



Na 2 G_. ..... 



16-77 



16-81 



16-79- 62 = -271 [. 279 -0 97-l 

 19-H 23 = -008f 279 -° J7_i 



Li 2 



0-20 



0-19 



H 9 0... .... 



0-40 



0-45 



0-43 



Insol. . 0-81 



0-81 



0-81 



0-81 

 10050 







i 



ii i ii 



j formula is 



therefore 



K 2 0. 



2RO . P 2 5 or RRP0 4 , or essen- 



tially JSaMnP0 4 . It will be noticed that iron is present in 

 very small amount only (3 p. c.) and of lithia there is hardly 

 more than a trace (0*2 p. c). With the discovery of natrophil- 



